U.S. Department of the Interior

U.S. Geological Survey

New Studies Initiated by the U.S. Geological Survey—

Effects of Nutrient Enrichment on Stream Ecosystems 

By Mark D. Munn and Pixie A. Hamilton

FS-118-03

December 2003

In 2001, the U.S. Geological Survey’s 

National Water-Quality Assessment 

(NAWQA) Program began an intensive 

study of nutrient enrichment—elevated 

concentrations of nitrogen and phosphorus—in streams in five agricultural basins 

across the Nation (see map, p. 2). This 

study is providing nationally consistent 

and comparable data and analyses of 

nutrient conditions, including how these 

conditions vary as a result of natural and 

human-related factors, and how nutrient conditions affect algae and other 

biological communities. This information will benefit stakeholders, including the U.S. Environmental Protection 

Agency (USEPA) and its partners, who 

are developing nutrient criteria to protect 

the aquatic health of streams in different 

geographic regions. 

Nutrient enrichment is one of five 

national priority topics addressed by 

NAWQA in its second decade of studies, which began in 2001. During its first 

round of assessments in 51 major river 

basins (referred to as “Study Units”), 

NAWQA scientists collected data on 

water chemistry, stream hydrology and 

habitat, and biological communities; 

currently, NAWQA is revisiting selected 

basins and focusing on (1) trends, (2) factors that affect water quality and aquatic 

health, and (3) national priority water 

issues related to, for example, the development of nutrient criteria, source-water 

protection strategies, and stream restoration plans. 

The nutrient enrichment study has four 

major objectives that address nutrient 

conditions, dissolved oxygen, aquatic 

communities, and geographic and landscape features in agricultural basins (see 

inset). The focus on agricultural streams 

is a starting point. As the study progresses, streams draining other land uses, 

such as those in residential and urban 

areas, will likely be added.

Objectives of the nutrient 

enrichment study

1. Determine the total algal biomass 

and the abundance, type, and 

diversity of algal and aquatic insect 

communities in streams with different nutrient conditions, watershed 

characteristics, habitat, climate, and 

other natural factors.

2. Determine the interrelations among 

nutrient conditions, algal communities, and stream metabolism, which 

is defined as the gain and loss in 

dissolved oxygen associated with 

photosynthesis and plant and animal 

respiration. Adequate levels of dissolved oxygen are critical to fish 

and other aquatic life.

3. Determine the transport, chemical transformation, and retention 

of nutrients (referred to as “nutrient cycling”) in the water column 

and surrounding sediments, and 

resulting effects on biological communities in stream reaches. Such 

cycling differs in different geologic 

and hydrologic settings, and is 

controlled, in large part, by groundwater and surface-water interactions. 

4. Determine the extent to which associations between nutrient conditions 

and biological communities occur 

over geographic regions that share 

common natural features, landscape 

characteristics, and biological communities.

Nutrient Issues in Surface 

Water 

• Nitrogen and phosphorus are 

essential for healthy plant and animal populations, with each water 

body requiring the right balance of 

nutrients to maintain aquatic life. 

• Elevated concentrations of nutrients can lead to excessive, often 

unsightly, growth of aquatic plants. 

Overgrowth of aquatic plants can 

clog water-intake pipes and filters 

and can interfere with recreational 

activities, such as fishing, swimming, and boating. Subsequent 

decay of aquatic plants can result 

in foul odors and taste.

• Excessive aquatic plant growth 

reduces dissolved oxygen in water 

and alters stream habitat, both of 

which are critical for fish and other 

aquatic life. These problems occur 

locally and in receiving coastal 

waters where they can threaten fish 

and shellfish that are economically 

and ecologically important.

Excessive nutrients can cause overgrowth 

of algae and aquatic plants in streams, such 

as in this stream in the Apalachicola-Chattahoochee-Flint River Basins. USGS is studying 

nutrient enrichment and its effect on biological 

communities in diverse stream ecosystems 

across the Nation.

Printed on recycled paper
What is nutrient enrichment? 

Although the term “enrichment” usually has positive connotations, nutrient 

enrichment in our rivers, lakes, and 

estuaries is causing substantial ecological and economic problems across the 

Nation. These elevated concentrations of 

nutrients can lead to excessive and often 

unsightly growth of aquatic plants (algae 

and other plants). These plants can clog 

water-intake pipes and filters and interfere with fishing, swimming, and boating. 

Decaying aquatic plants can produce foul 

odors and can affect how water tastes. 

By decreasing oxygen concentrations 

and altering stream habitat in the water, 

aquatic plant overgrowth also can be 

harmful to fish and other aquatic organisms. 

Nutrient enrichment and its associated problems can extend from local 

waters to downstream waters, including coastal environments. For example, 

elevated nutrient concentrations in 

streams throughout the Midwest contribute to water-quality problems in the 

Gulf of Mexico. Estuarine and shallow 

marine environments in the Gulf often are 

impaired by massive algal blooms, largescale oxygen “dead zones,” degraded sea 

grass beds and coral reefs, and outbreaks 

of harmful organisms. The consequences 

include losses to aquatic life, which 

affects fishing and other water industries, 

reduced recreational opportunities, and a 

lower aesthetic quality of our waters.

A 1998 national inventory of water 

quality conducted by States and Tribes 

found that nutrients were a leading cause 

of water-quality impairment in our rivers, 

lakes, and estuaries. Elevated concentrations of nutrients were found in 10 

percent of assessed rivers and streams 

(about 840,000 river and stream miles 

were assessed), and contributed to 30 percent of reported water-quality problems 

in the impaired rivers and streams (about 

291,000 miles). In 2000, the inventory 

found that nutrients were still a concern; 

as in 1998, runoff from agricultural land, 

which commonly carries with it high 

concentrations of nutrients, was the number one cause of water-quality problems 

in assessed rivers and streams (about 

700,000 river and stream miles were 

assessed) (U.S. Environmental Protection 

Agency, 2000; 2002). 

Responding to the Nutrient 

Enrichment Problem

It has been difficult to craft a national 

response to this issue, such as a set of 

widely applicable management strategies 

and policies, because nutrient enrichment is widespread, complex, and highly 

variable. Nutrient conditions—a term that 

encompasses sources of nutrients, their 

concentrations in soil and water, their 

transport, and their uptake by plants and 

animals—vary seasonally and among 

watersheds. Nutrient conditions are 

affected by climate, soil type, amount of 

ground-water discharge to streams, characteristics of the streambed, amount of 

riparian shading, physical disturbance of 

stream habitat, and biological organisms. 

How streams respond to nutrient enrichment varies depending on these factors, 

and the rate at which streams can recover 

following implementation of management strategies also varies. 

White, Great and Little Miami

River Basins (WHMI)

Potomac River Basin and

Delmarva Peninsula

(PODL)

Central Columbia PlateauYakima River Basin (CCYK)

Central Nebraska

Basins (CNBR)

ApalachicolaChattahoocheeFlint River Basins

(ACFB)

Nutrients are studied in stream 

ecosystems across the Nation

The five Study Units (including parts 

of nine States) in the nutrient enrichment study are the Apalachicola-Chattahoochee-Flint River Basins (Georgia 

and Florida); Central Columbia Plateau-Yakima River Basin (Washington); 

Central Nebraska Basins (Nebraska); 

Potomac River Basin and Delmarva 

Peninsula (Maryland, Delaware, and 

Virginia); and the White, Great and Little 

Miami River Basins (Indiana and Ohio). 

Similar studies in additional basins will 

begin in 2004 and 2007. A consistent, 

two-fold study approach is being used. 

First, streamflow, nutrient concentrations and other chemical characteristics, dissolved oxygen concentrations, 

biological communities, and stream and 

riparian habitat are assessed at 25-30 sites 

within each Study Unit. Data from these 

one-time “snapshot” assessments will be 

used to define relations among nutrients, stream metabolism, and biological 

communities in diverse environmental 

settings (study objectives 1 and 2, see 

p.1), and to aid in statistical analyses for 

regionalization of nutrient conditions 

(objective 4).

Second, processes controlling stream 

metabolism and nutrient cycling (which 

includes transport, transformation, and 

retention) are being assessed in a single 

stream reach within three of the five 

Study Units. These more detailed, smallscale studies will help to determine the 

effects of these processes on biological 

communities (objectives 2 and 3), and 

help to identify environmental settings 

that have chemical, physical, and biological characteristics associated with nutrient enrichment (objective 4). 

Effects of nutrient enrichment on stream 

ecosystems are being investigated in 5 of 14 

NAWQA Study Units: the Apalachicola-Chattahoochee-Flint River Basins; Central Columbia 

Plateau-Yakima River Basin; Central Nebraska 

Basins; Potomac River Basin and Delmarva 

Peninsula; and the White, Great and Little 

Miami River Basins. 
How USGS information is used

Improved standards and guidelines for 

protecting aquatic and human health

As of 2003, only one enforceable national 

standard for nutrients exists—10 milligrams per liter of nitrate (as nitrogen) 

in drinking water—to protect human 

health. USEPA has established a nonregulatory desired goal of 0.1 milligram 

per liter of total phosphorus in surface 

water—to prevent overgrowth of algae 

and aquatic plants in streams and other 

flowing waters not discharging to lakes or 

impoundments. USEPA is continuing to 

develop criteria for total phosphorus and 

total nitrogen in streams for the protection of aquatic and human health, and is 

focusing on different geographic regions 

and types of water bodies; the goal is to 

have criteria that are congruent with State 

water-quality standards. USGS findings on nutrient conditions, biological 

communities, stream characteristics, and 

environmental settings are being used in 

the development of these regional nutrient criteria. 

Improved State assessments of beneficial 

uses and impaired streams

States and Tribes use USGS nutrient 

findings for state assessments of benThe five Study Units 

settings (climate, geology, topography, and soils) and agricultural practices (crop and animal production and irrigation and drainage practices)

Study Unit Major crop and animal 

production

Primary agricultural 

management practices

Hydrologic setting Key factors affecting 

nutrient transport

ApalachicolaChattahoochee-Flint 

River Basins

Row crops and poultry Moderate irrigation 

(center pivot); widespread use of modified 

ditches and dredged and 

channeled streams

Humid; moderately permeable soilsRelatively intact and extensive riparian zones and 

forested wetlands; groundwater discharge

Central Columbia PlateauYakima River BasinCattle grazing, row crops, 

orchards, vineyards, and 

some dairy

Irrigation (pivot, furrow, 

and drip); widespread 

use of irrigation canals 

and artificial drainage

Arid; deep loess soils 

underlain by basalt

High hydrologic management (irrigation withdrawals 

and return flows); seasonal 

variability in turbidity, flow, 

and ground-water discharge; 

limited stream shading

Central Nebraska Basins Row crops and some 

dairy

Center pivot irrigation Semiarid; permeable 

surface and subsurface

Ground-water discharge; 

poorly shaded streams with 

seasonally high turbidity

Potomac River Basin and 

Delmarva Peninsula

Row crops, poultry, and 

some dairy

Tillage and no tillage; 

some center pivot irrigation

Humid; moderately to 

well-drained soils; permeable sand and gravel 

surficial aquifer

Ground-water discharge with 

low turbidity and well-shaded streams

White, Great and Little 

Miami River Basins

Row crops Tillage and no tillage; 

widespread use of artificial drainage (tile drains 

and ditches)

Humid; poorly-drained 

soils; relatively impermeable glacial till and 

sediment

Overland runoff; tile drains; 

highly turbid streams

Data on streamflow, nutrient concentrations and other chemical characteristics, dissolved oxygen, biological communities, and stream and riparian habitat are collected at 25–30 sites within 

each of the Study Units.

eficial uses of streams for aquatic life, 

recreation, and drinking water (required 

in USEPA 305(b) reports), and to help 

determine the level of stream impairment 

(required in USEPA 303(d) reports). For 

example, the New Jersey Department of 

Environmental Protection used NAWQA 

findings in preparing their 305(b) reports, 

which documented long-term trends in 

nitrate contamination and changes in 

stream conditions and fish communities in northern New Jersey as a result of 

improved wastewater treatment. USGS 

findings on nutrient concentrations, 
and geographic regions for land management, leading to more focused and 

effective strategies and monitoring. The 

findings also can help managers design 

more effective strategies for nutrient 

management. For example, understanding 

the relative effects of nutrient enrichment and physical stream disturbance 

on biological communities can help 

water managers decide whether to direct 

resources towards managing chemical use 

and nutrients or towards restoring stream 

habitat.

The USGS promotes public access 

to water-quality information 

Visit the NAWQA Web site to access 

reports, water-quality data, and maps:

http://water.usgs.gov/nawqa 

Visit the EPA Web site to access information on nutrient criteria:

http://www.epa.gov/waterscience/standards/nutrient.html

and for biennial national water quality 

inventory reports:

http://www.epa.gov/305b/

For additional information and 

questions, please contact:

Mark D. Munn, Team Leader, 

Nutrient Enrichment Effects study 

(253) 428–3600 ext. 2686 

mdmunn@usgs.gov 

W. Brian Hughes, Lead Scientist, 

Apalachicola-ChattahoocheeFlint River Basins (770) 903–9162 

wbhughes@usgs.gov

http://ga.water.usgs.gov/nawqa/

Robert W. Black, Lead Scientist, 

Central Columbia Plateau-Yakima 

River Basin (253) 428–3600 ext. 2687 

rwblack@usgs.gov

http://wa.water.usgs.gov/projects/ccyk/

Ronald B. Zelt, Lead Scientist, Central 

Nebraska Basins (402) 437–5157

rbzelt@usgs.gov

http://ne.water.usgs.gov/Nawqa/index.

htm

Judith M. Denver, Lead Scientist, 

Potomac River Basin and Delmarva 

Peninsula (302) 734–2506 ext. 229

jmdenver@usgs.gov

http://md.water.usgs.gov/pnawqa/

Jeffrey W. Frey, Lead Scientist, White, 

Great and Little Miami River Basins 

(317) 290–3333 ext. 151

jwfrey@usgs.gov

http://in.water.usgs.gov/nawqa/

wrnawqa.htm

Literature cited

U.S. Environmental Protection Agency, 

2000, National Water Quality Inventory: 1998 Report, U.S. Environmental 

Protection Agency Report EPA–841–

R–00–001, Washington, D. C.

U.S. Environmental Protection Agency, 

2002, National Water Quality Inventory: 2000 Report, U.S. Environmental 

Protection Agency Report EPA–841–

R–02–001, Washington, D. C.

The NAWQA Program

USGS nutrient enrichment studies are planned and implemented through the 

National Water-Quality Assessment (NAWQA) Program (a map is available at 

http://water.usgs.gov/nawqa). In 1991, NAWQA began evaluating the quality 

of streams, ground water, and aquatic ecosystems in 51 major river basins and 

aquifer systems (known as “Study Units”) across the Nation. The assessments 

characterize the ambient water resource—the source of about 60 percent of the 

Nation’s drinking water and water for industrial, irrigation, and recreational uses. 

During its first decade, NAWQA made baseline assessments of pesticides, nutrients, volatile organic compounds, trace elements, dissolved solids, and radon, as 

well as the condition of aquatic habitats and fish, insect, and algal communities. 

These findings are described in numerous reports (these reports can be accessed at 

the NAWQA Web site above). 

During the next decade of studies, 42 of the Study Units will be intensively 

reassessed to determine trends at many of the streams and ground-water monitoring sites; fill critical gaps in characterizing water-quality conditions; and 

build upon earlier NAWQA findings that show how natural features and human 

activities affect water quality and aquatic ecosystems. Nutrient enrichment is 

one of five national priority topics that will be addressed in the second decade 

of NAWQA studies. The four other topics include (1) effects of urbanization on 

stream ecosystems; (2) bioaccumulation of mercury in stream ecosystems; (3) 

transport of contaminants to public-supply wells; and (4) sources, transport, and 

fate of agricultural chemicals.

sources, transport, and loads also can 

help in the development of TMDLs, or 

Total Maximum Daily Loads. NAWQA 

findings on naturally elevated concentrations of phosphorus transported in 

ground water to surface water in parts of 

the Albemarle-Pamlico Sound Drainage 

Basins were used in developing TMDLs 

for selected North Carolina streams.

Improved ecological indicators and 

monitoring

USGS assessments are useful in identifying ecological indicators of nutrient 

enrichment and associated water-quality issues. Improved understanding of 

key indicators will help water managers 

prioritize streams for protection and 

restoration, reduce monitoring costs, and 

evaluate strategies for reducing nutrients 

in streams. USGS nutrient assessments 

also can help to determine whether 

biological assessment techniques used by 

States, consultants, and other stakeholders are sufficient for evaluating the health 

of streams and restoration efforts.

Improved identification of high-priority 

streams, regions, and appropriate 

management strategies

USGS assessments of regional variations 

in nutrient conditions can help resource 

managers establish and prioritize streams